1. Field of the Invention
The present invention relates to lithographic projection apparatus and more particularly, to interferometric lithographic projection apparatus (both immersion and non-immersion).
2. Related Art
Usually a lithographer, when printing test line patterns (or test contact hole patterns), prefers to print several sets of lines, starting with the finest resolution, and ending with the larger lines and/or contact holes. This is because the resolution of the overall semiconductor manufacturing process depends not only on the optics involved, but also on the chemical processes, and the interactions between the photoresist, and the etching chemicals, etc. Thus, a lithographer often needs to know at which resolution the etching of the photoresist begins to break down.
When resolutions reach nanometer scale, such as 30-100 nm, it is very difficult to use conventional masks and reticles to accomplish this. Also, utilizing a conventional lithographic projection apparatus, that uses reticles and lenses is extremely expensive, since such projection apparatus, particularly projection apparatus at the extreme limits of resolution often cost in the range of $5 to $20 million. The current resolution limit of lens-based lithographic projection apparatus is approximately 65 nm, and even reaching this resolution is considered a difficult accomplishment at the current state of the art.
Many of the current lithographic projection apparatus available for interferometric lithographic printing may be better in printing at a resolution lower than conventional lithography projection apparatus however interference lithography projection apparatus are not capable of printing different patterns at different resolutions.
Accordingly, there is a need in the art for an interferometric lithographic projection apparatus that has the ability to print multiple patterns.